Embodiments of the present invention relate to processing of a substrate with rapid temperature gradient control across the substrate.
In the processing of substrates, such as semiconductors and displays, an electrostatic chuck is used to hold a substrate in a chamber for processing of a layer on the substrate. A typical electrostatic chuck comprises an electrode covered by a ceramic. When the electrode is electrically charged, electrostatic charges accumulate in the electrode and substrate, and the resultant electrostatic force holds the substrate to the chuck. Typically, the temperature of the substrate is controlled by maintaining helium gas behind the substrate to enhance heat transfer rates across the microscopic gaps at the interface between the back of the substrate and the surface of the chuck. The electrostatic chuck can be supported by a base which has channels for passing a fluid therethrough to cool or heat the chuck. Once a substrate is securely held on the chuck, process gas is introduced into the chamber and a plasma is formed to process the substrate. The substrate can be processed by a CVD, PVD, etch, implant, oxidation, nitridation, or other such processes.
In such conventional substrate fabrication processes, the substrate is maintained at a single temperature during processing. Typically, the substrate is passed through a slit in the chamber by a wafer blade and deposited on lift pins which are extended through the body of the electrostatic chuck. The lift pins are then retracted back through the chuck to deposit the substrate on the surface of the chuck. The substrate quickly rises in temperature to a preset temperature which is then maintained steady by heaters in the chuck or by the plasma formed in the chamber. The substrate temperature can be further controlled by the temperature and flow rate of coolant passed through the channels of the base and below the chuck which is used to remove heat from the chuck.
While conventional processing chamber are suitable for maintaining the substrate at a steady single temperature during processing, they do not allow rapid changing of the temperature of the substrate during a single process cycle. In certain processes, it is desirable to rapidly ramp up or down the substrate temperature, to achieve a particular temperature profile during the process. For example, it can be desirable to have rapid changes in substrate temperature at different stages of an etching process to allow etching of different materials on the substrate at different substrate temperatures. At these different etching stages, the process gas provided to the chamber can also change in composition or have the same composition. As another example, in etching processes, such a temperature profile may be useful to deposit sidewall polymer on the sidewalls of the features being etched on the substrate, and later in the same etching process, remove the sidewalk polymer by increasing the temperature of the etching process, or vice versa. Similarly, in deposition processes, it may be desirable to have a first processing temperature which is higher or lower than a second processing temperature, for example, to initially deposit a nucleating layer on the substrate and then grow a thermally deposited layer on the substrate. Conventional substrate processing chambers and their internal components often do not allow sufficiently rapid ramp up and down of substrate temperatures.
A further complication arises when, during processing, the substrate is subjected to non-uniform process conditions in a radial direction across the substrate which can give rise to non-uniform, concentric processing bands. The non-uniform processing conditions can arise from the distribution of gas or plasma species in the chamber, which often varies depending on the location of the inlet and exhaust gas ports in the chamber. Mass transport mechanisms can also alter the rate of arrival or dissipation of gaseous species at different regions of the substrate surface. Non-uniform processing can also occur as a result of non-uniform heat loads in the chamber, arising for example, from the non-uniform coupling of energy from a plasma sheath to the substrate or from radiant heat reflected from chamber walls. The processing bands and other variations across the substrate are undesirable as the electronic devices being fabricated at different regions of the substrate, for example, the peripheral and central substrate regions, end up with different properties. Accordingly, it is desirable to reduce the variations in processing rates and other process characteristics across the substrate surface during processing of the substrate.
Thus it is desirable to have a process chamber and components that allow rapid temperature ramp up and down of the substrate being processed in the chamber. It is further desirable to control temperatures at different regions across the processing surface of the substrate to reduce the effect of non-uniform processing conditions across the substrate surface in the radial direction. It can also be desirable to control the temperature profile across the substrate during processing.